Actuators are commonly used in a variety of contexts to control devices. For example, actuators are used in heating, ventilating, and air-conditioning (HVAC) systems to actuate a variety of loads, such as opening and closing dampers and valves.
Typically, an actuator is designed with a rating that specifies a maximum torque at which the actuator is capable of actuating the load. Preferably, the actuator is capable of generating the rated maximum torque, but is also configured not to exceed the rated maximum torque. If the rated maximum torque is exceeded, it is possible for the actuator to damage the load and/or the gear train or linkage connected between the actuator shaft and the load.
It is also desirable to precisely control the positioning and velocity of the actuator as the actuator actuates a load from a first to a second position. Actuators can use one or more feedback loops to control the actuator during actuation. For example, some actuators use a positional feedback loop, which monitors a position of an actuator's motor relative to a desired end position. The error between the actuator's present position and the desired end position is calculated by a controller, which uses this error to direct the actuator's motor to the desired end position.
Other actuators employ a velocity feedback loop, which monitors a velocity at which an actuator's motor is currently operating. An error between the actuator's current velocity and desired velocity is calculated by a controller, which then uses this error to speed or slow the velocity of the actuator as desired.
A typical actuator used in an HVAC system includes a spring return to drive a load such as a damper or valve coupled to the actuator back to an initial or closed position. The spring return includes a spring that is wound by the actuator's motor as the actuator opens the damper, and the energy stored in this spring is used to return the damper to the initial position upon loss of power.
Further, some HVAC actuators (typically called modulating actuators) are configured to stop at positions between the fully closed and fully open stops. Such actuators must therefore develop sufficient torque to, for example, overcome the spring returns incorporated into the actuators, while opening or holding at the intermediate position short of the fully open stop.
Control of the rated maximum torque and positioning and velocity of an actuator can be complicated by variances in the tolerances between actuators, as well as by the need to overcome the spring return. In addition, control can be complicated by the necessity in modulating actuators to stop at intermediate positions between fully open and fully closed stops.
While the positional and velocity types of feedback control loops for actuators are sufficient for some applications, the prior art control designs for actuators do not always provide the desired efficiency and precise control needed. Therefore, it is desirable to provide new systems and methods for controlling the actuation of an actuator.